HP and gearing may indicate the maximum speed a vehicle can ultimately reach and sustain, but torque determines how fast it will reach it.

90Brougham350

11-07-06, 05:06 PM

Exactly. Horsepower doesn't determine how fast a car is. Peak torque, peak torque RPM, and width of the power curve determine how fast a car is along with the gearing.

eldorado1

11-07-06, 05:27 PM

I'm not confused...

HP and gearing may indicate the maximum speed a vehicle can ultimately reach and sustain, but torque determines how fast it will reach it.

Really? Because in that article, it showed a 550 ft-lb cummins diesel being beat by a 290 ft-lb formula 1 engine....

I think you're still confusing torque *at the wheels* with torque at the flywheel.

eldorado1

11-07-06, 05:28 PM

-Peak torque
-peak torque RPM
-and width of the power curve determine how fast a car is
-along with the gearing.

No
No
YES
YES!

danbuc

11-07-06, 07:54 PM

Really? Because in that article, it showed a 550 ft-lb cummins diesel being beat by a 290 ft-lb formula 1 engine....

I think you're still confusing torque *at the wheels* with torque at the flywheel.

It's a little hard to compare a Diesel who's power band may span 2000k rpm, and a high winding small displacement V10 who's power band can easily reach into the 15k rpm range. You put that High-winding V10 into a Dodge Ram, and line it up to another Dodge Ram equipped with the Cummin's diesel, and tell me which one is faster. Something tells me that diesels got he V10 beat.

As for the F1 Honda being faster than the deisel it's quite easy to explain why. With it's 18k+ rpm power band, the V10 in the Honda has the HP to carry that torque up through the rpm range. Sure it's probably no the flatest torque curve around but it makes due.....plus it's idles around 10k (so it's really only got an 8k rpm power band per say). Now that Cummins diesel has make it's peak hp around 2krpm, and it's peak torque is mostly like around 1500. It's doesn't have the ability to carry that torque up through the RPM range like the Honda motor does, that's why it relies on short shifts, and a taller final drive. Also, the Cummins Diesel is not a thorough-bread race engine. It is a big torque, low RPM beast of a motor, designed for the soul purpose of making huge power, and low rpm/speed. So yeah, it's gonna be an ass load slower than the crappy Honda V10. Your not gonna pull any tree stumps out with that V10 I can assure you that.

That article only begs the question....do people really think about what they are saying before they say it? I say, that article is a good example of a maybe he did, maybe he didn't...who knows type of situation.

I'll end with this. Torque, is the engine ability to turn the driveshaft, which turn the axle, which then in turn spins the wheel....so, Torque is the engine ability to turn the wheels.

HP, is the engine's ability to carry that torque up the RPM range, making it usable at higher speeds.

The acceleration your feel in your ass when you nail the throttle....that's torque. The more of it you have, the harder the engine's going to turn the wheel. The more hp you have, the faster the engines going to turn the wheels. Without torque, the engine has to work much harder to reach a give speed. Without HP, it takes a longer time to reach that speed, but will be done with much less effort.

Ranger

11-07-06, 08:00 PM

The Guru once posted a very lengthy and detailed (as usual) explanation. He pretty much said what Danbuc is saying. I remember him saying "People buy HP, but drive torque".

danbuc

11-07-06, 08:13 PM

What people don't realize it that's it's all relative. In some applications (like heavy utilitarian vehicles designed for towing and pushing) lot's of hp is not necessary. All they need is lot's of low end torque to proved the brute force needed to do heavy work. In other applications (like that of the F1 car) lots of torque isn't necessary, since it's not really pulling/pushing much weight, and isn't required to do much work. All it has to is spin the tires really fast.

Some vehicle need more low-rpm torque. Other's benefit from high-rpm HP. There's no way to say one's better than the other. Each has it's strong points in certain applications. Sadly, our heavy cars could benefit from more low end torque, which would help out in the acceleration department as it were. Other vehicles, like a 396 Chevelle have all the torque they need, but could benefit from a little more top end power. It's all application specific.

eldorado1

11-07-06, 09:51 PM

It is a big torque, low RPM beast of a motor, designed for the soul purpose of making huge power, and low rpm/speed. So yeah, it's gonna be an ass load slower than the crappy Honda V10. Your not gonna pull any tree stumps out with that V10 I can assure you that.

Now I can TELL you didn't even read the article.

How can I tell? Because again, you're neglecting gearing. You can take a motor from a VCR, and with enough gears, you could pull a tree stump out. Or lift a 500 pound safe 1' off the ground.. It would take days (years?) because it doesn't have enough horsepower, but it could do it.

Power = Force * Distance / Time

To quote the article:

To accurately describe the acceleration capability of your vehicle, we must consider time. If we just considered force, and distance, we wouldn’t really be saying much about the car. If I tell you that my car can pull a 3,000-lb. weight 100-ft. up a hill, would you be impressed? Certainly not, because I haven’t really told you much. If I told you that I could do it in 10 seconds, while your car needed 15 seconds to do the same job, you might be impressed.

Torque's a force.

BTW, keep it coming, I like these discussions, as long as you keep it civil.

1997BlackETC

11-07-06, 10:24 PM

Now the question is, how to get more torque out of the northstar. My 4.9 is a joy to drive around because of all the low end grunt, my northstar is a joy to drive on the highway because of the top end horsepower, maybe I should just stuff a 4.9 in the trunk :)

chevelle

11-07-06, 11:25 PM

I good practical comparison of torque and HP is to consider yourself riding a 10 speed bike up a hill. Put it in the lowest gear and you can move the pedals easily but you won't go very fast unless you can pedal at a very fast rate and keep it up forever. On the other hand, you could move to a higher gear. It would get harder to pedal but you would be moving faster. In the first example you would be the high HP, high revving F1 engine. Not much torque but the gearing makes up for it and the engine can rev hard enough to make up the speed lost thru gearing. In the second case you would be the Duramax diesel slogging up the hill with tons of torque.

The difference is not as easy as just explaining torque and HP and then compare engines on a one-to-one basis. Sure, the F1 engine can pull as much weight up the hill with the correct gearing. But can it live for hundreds and thousands of hours revving at 18,000 RPM to do that? No. The big diesel won't win any races with all that torque necessarily but it can pull hills for hours on end making max torque. Two different applications and two different power requirements. Not very comparible.

HP is useful for comparing the outputs of dramatically different engines on the same scale, though.

Just pulling a load up a hill and accelerating a load are also two different things and that also doesn't get addressed in the usual HP vs. Torque discussion.

The diesel can pull a heavy load with all the torque it makes but it has a very narrow power band. Duramax diesels sign off at about 3500 and class 8 diesels rarely rev over 2400. This requires lots of gear changes to keep the engine in it's torque band. A higher revving gasoline engine can often accelerate quite well even with a heavy load with the right gearing due to it's ability to rev to a very high RPM which makes the power band (and the area under the curve of the torque/HP graph) quite a bit wider.

eldorado1

11-08-06, 08:16 AM

Good points.

Perhaps a more "level" race would be between an LT1 and an L98 powered car. It doesn't illustrate the difference as well, but the LT1 and L98 both make the same amount of peak torque, but different HP. The LT1's a breather...

dp102288

11-08-06, 09:55 AM

Excellent thread. Keep them coming. I love it.

danbuc

11-08-06, 05:32 PM

I read the article, but saying it's only a matter of gearing between the V10 pulling a tree out of the ground, or pushing a car to 200+mph is crap. I guess if I tied a big enough block&tackle to an ant's ass, I could come up with some gear ratio that would allow him to lift the white house....but it doesn't mean anything, because it'll never happen. The gears used in a vehicle, and it's power band (hp and torque curves) are usually designed as a package deal. You don't build an engine and then say, "Let's see what kinda gears we can throw behind this thing". Both have to be carefully selected for their particular application.

eldorado1

11-08-06, 06:19 PM

saying it's only a matter of gearing between the V10 pulling a tree out of the ground, or pushing a car to 200+mph is crap.

But it's the truth.

You're right in that they're not going to build a racing engine to run at 10,000 rpm to pull a semi. There are other tradeoffs such as longevity that trump that as chevelle mentioned.

But one engine can be made to pull stumps or race - assuming it has the proper gearing and horsepower.

JimHare

11-08-06, 06:51 PM

But one engine can be made to pull stumps or race - assuming it has the proper gearing and horsepower.

Very interesting conversation. I need to reread the info to be sure I truly understand both points

danbuc

11-08-06, 09:51 PM

But it's the truth.

You're right in that they're not going to build a racing engine to run at 10,000 rpm to pull a semi. There are other tradeoffs such as longevity that trump that as chevelle mentioned.

But one engine can be made to pull stumps or race - assuming it has the proper gearing and horsepower.

This is true....that Cummins straight 6 can get goin' pretty fast in the right truck with the right mods. I raced and lost to a friend of mine at school who had a chipped F250.....that thing was a beast.

Definitely a workhorse if I ever saw one. Never know when I might have to haul a cement mixer home, to build the new Olympic sized swimming pool in the living room of my 400k square foot castle.

GreenMachine

11-08-06, 10:17 PM

For this comparison to truly work you need an engine that has the SAME redline (MAX) RPM.

Cap that Cummins at 18,000 RPM and see what its numbers look like.

Now cap that Honda F1 Engine at the 3500-4000? or so RPMs the Cummins maxes out at.

You have a pretty weak engine.

Alright, now why do you think the automakers have jumped on the Variable Valve Timing (VVT, Valvetronic etc) bandwagon? You need the High HP for the top speed, but you need the low end grunt to get the vehicle to those speeds in a reasonable time period.

HP is the measurement of torque over time. So when lets say the Northstar is twisting at a 5500 RPMs and you holding the throttle down, the car needs to switch gears since its past it HP peak since it can no longer produce enough torque to turn the gears. Dropping to the next gear lets you once again rev threw the power band.

See what I'm saying? That 18,000 RPM race car WILL NOT accelerate as fast from 180mph to 190mph as it would 80mph-90mph because your using such a large gear at that point and have exhausted your available torque.

I think that all makes sense.

danbuc

11-08-06, 10:31 PM

If the L37 engine had VVT it would have a much broader, flatter torque curve and would have to suffer as badly with the various dead spots it has. 40mph, and 80mph are the two big ones. Bottom of second, and bottom of third gear.

GreenMachine

11-08-06, 10:40 PM

If the L37 engine had VVT it would have a much broader, flatter torque curve and would have to suffer as badly with the various dead spots it has. 40mph, and 80mph are the two big ones. Bottom of second, and bottom of third gear.

Probibly why they made the the LH2 to begin next generation of Northstars and mated it to a 5 or 6 speed. As I always say, these cars are great, but being FWD and so big, it makes them somewhat not appealing to most performance seekers. When compared to other Luxury Full-Sized (Large) Sedans they stack pretty well (actually for the "everyday" sedan segment they are creme of the crop). For Northstar based vehicles, the DTS continues that trend of being the best of the big ones (and other smaller family type sedans), the STS has been reworked into a RWD true performance sedan that it should have always been and gets up to 60 in 5.8 seconds where as the past STS[Seville] are mid 6's on a lucky day.

eldorado1

11-09-06, 10:58 AM

Alright, now why do you think the automakers have jumped on the Variable Valve Timing (VVT, Valvetronic etc) bandwagon?

Larger powerband.

HP is the measurement of torque over time. So when lets say the Northstar is twisting at a 5500 RPMs and you holding the throttle down, the car needs to switch gears since its past it HP peak since it can no longer produce enough torque to turn the gears. Dropping to the next gear lets you once again rev threw the power band.

Lets say you have a northstar made of unobtanium, and it revs to 20k without blowing up. It's "stock", in that it makes 300hp @ 6000rpm. You are going to drag race, and are in 1st gear.

Light turns green, you floor it. Revs are climbing... 3000.... 4000... 5000.... When should you shift? You shift when you're making the same power as the next gear would start. So here's your HP graph:

http://www.caddyinfo.com/46_tc.jpg
Lets assume it's a linear drop from 300hp @ 6000rpm. I'd say at 9000rpm, you're making 250hp. (not true in real life, but assuming a linear fall off here)... So you keep pulling until 9000rpm, and you shift.

At this point, if you're using a 4t80e, you're at 60mph and 2nd gear puts you at 5000rpm. 5000's about 275hp, so you went a little long, but you get the idea. You want to maximize the amount of HP reaching the wheels, for the longest amount of time.

See what I'm saying? That 18,000 RPM race car WILL NOT accelerate as fast from 180mph to 190mph as it would 80mph-90mph because your using such a large gear at that point and have exhausted your available torque.

That applies to any car/truck/thing...

A diesel from a semi will not accelerate as fast from 50-60 as it would from 20-30. As speeds increase, accelerations decrease. There are exceptions, like jet powered vehicles, which have constant accelerations...

GreenMachine

11-10-06, 04:53 PM

That applies to any car/truck/thing...

A diesel from a semi will not accelerate as fast from 50-60 as it would from 20-30. As speeds increase, accelerations decrease. There are exceptions, like jet powered vehicles, which have constant accelerations...

That my point exactly, punch the throttle at your torque max, then punch it at your HP max, you gonna accelerate much quicker at the peak torque spot than the max HP spot.

Those formual one engines probibly don't even have the clutch in until 4000+ RPMs.

To succesfully have a "fast" car you need alot torque in the low, and alot of HP in the high end, torque accelerates, gets it moving, HP is what keeps it going up and up over time. Thats the theory behind the LS6/7 engines and holds true for the northstar of a balanced approach.

For performance street cars you need both,
For things that pull stuff out of the ground, you need torque
For racing cars with less than 1000lbs of weight, you need enough to get the car moving, but mostly HP to keep it going up and up. Ultimatley HP determines top speed, torque is then built off of that for the application.

davesdeville

11-11-06, 10:10 PM

When we have a CVT that can handle a decent amount of power I might start taking note of high RPM power. Until then we're stuck with gears and torque still rules.